In that case, **FastAPI** also provides you with the tools to build it.

///

When we create an instance of the `OAuth2PasswordBearer` class we pass in the `tokenUrl` parameter. This parameter contains the URL that the client (the frontend running in the user's browser) will use to send the `username` and `password` in order to get a token.

//// tab | Python 3.9+

```Python hl_lines="8"

    globalns = getattr(call, "__globals__", {})
    typed_params = [
        inspect.Parameter(
            name=param.name,
            kind=param.kind,
            default=param.default,
            annotation=get_typed_annotation(param.annotation, globalns),
        )
        for param in signature.parameters.values()
    ]
    typed_signature = inspect.Signature(typed_params)
    return typed_signature

Dieser Teil ist ziemlich normal, der größte Teil des Codes ist Ihnen wahrscheinlich bereits bekannt:

```Python hl_lines="9-13  36-53"
{!../../docs_src/openapi_callbacks/tutorial001.py!}
```

/// tip | "Tipp"

   * that conversion is safe.
   *
   * <p>This method is intended to help with usages of type parameters that have {@linkplain
   * ParametricNullness parametric nullness}. If a type parameter instead ranges over only non-null
   * types (or if the type is a non-variable type, like {@code String}), then code should almost

   * that conversion is safe.
   *
   * <p>This method is intended to help with usages of type parameters that have {@linkplain
   * ParametricNullness parametric nullness}. If a type parameter instead ranges over only non-null
   * types (or if the type is a non-variable type, like {@code String}), then code should almost

# Body – Felder

So wie Sie zusätzliche Validation und Metadaten in Parametern der **Pfadoperation-Funktion** mittels `Query`, `Path` und `Body` deklarieren, können Sie auch innerhalb von Pydantic-Modellen zusätzliche Validation und Metadaten deklarieren, mittels Pydantics `Field`.

## `Field` importieren

Importieren Sie es zuerst:

//// tab | Python 3.10+

```Python hl_lines="4"
{!> ../../docs_src/body_fields/tutorial001_an_py310.py!}
```

          .isEqualTo(Strings.lenientFormat("", Arrays.copyOfRange(params, 2, params.length)));
    }
  }

  /**
   * Returns an array containing parameters for invoking a checkArgument, checkNotNull or checkState
   * method reflectively
   *
   * @param firstParam The first parameter
   * @param sig The method signature
   */
  @GwtIncompatible("ArbitraryInstances")
  @J2ktIncompatible

                **Note**: you probably shouldn't use this parameter, it is inherited
                from Starlette and supported for compatibility.

                ---

                A list of routes to serve incoming HTTP and WebSocket requests.
                """
            ),
            deprecated(
                """
                You normally wouldn't use this parameter with FastAPI, it is inherited

 *
 * The query is optional: it can be null, empty, or non-empty. For many HTTP URLs the query string
 * is subdivided into a collection of name-value parameters. This class offers methods to set the
 * query as the single string, or as individual name-value parameters. With name-value parameters
 * the values are optional and names may be repeated.
 *
 * ### Fragment
 *

     * parameter type matches boolean primitive formal type). This behavior
     * is because this method is used to determine applicable methods for
     * an actual parameter list, and primitive types are represented by
     * their object duals in reflective method calls.
     *
     * @param formal the formal parameter type to which the actual